1. Background of the Invention
The present invention relates to a vacuum processing apparatus for processing a target object such as a semiconductor device, a method of supplying a processing gas such as a cleaning gas into the vacuum processing apparatus, and a method for cleaning the processing apparatus.
2. Description of the Related Art
In recent years, the integration density of a semiconductor integrated circuit element has increased, and the degree of integration has changed from the 64-M DRAM generation to the 256-M DRAM generation. For this reason, the number of layers of a wiring structure has more increased, and micropatterning thereof has become more conspicuous.
When the number of layers of the wiring structure increases as described above, the number of steps of a wiring process increases, and an increase in efficiency of the wiring process and dustproof measures therefor have posed problems more seriously than those of the conventional technique. In addition, with an increase in micropatterning level of the wiring structure, a migration disconnection becomes a problem in a conventional aluminum (Al) wiring structure. Therefore, as a wiring material replaceable with Al, a metal such as tungsten (W) having an excellent resistance to migration disconnection is variously examined. In addition, inorganic-based materials and an organic-based materials are used to these materials.
Conventionally, an inorganic-based compound and an organic-based compound are used for the wiring and insulating materials. Some organic-based compounds such as a carbonyl compound are gaseous at room temperature, but many organic-based compounds such as an alkyl metal compound are liquid at room temperature. In contrast to this, many inorganic-based compounds are gaseous at room temperature. For example, tungsten hexafluoride (WF.sub.6 : b.p. 17.2.degree. C.), dichlorosilane (SiH.sub.2 Cl.sub.2 : b.p. 8.2.degree. C.), chlorine trifluoride (ClF.sub.3 : b.p. 11.75.degree. C.), and the like have relatively higher boiling points in inorganic-based compounds, and they are liquid within the range of 0.degree. C. to room temperature. These inorganic-based compounds are often used for a film formation process or an etching process. Conventionally, when these inorganic-based compounds are used for a film formation process, such an inorganic-based compound is heated to be completely gasified as a processing gas for a film formation process or the like. Then, the gas is supplied into a processing chamber by adjusting the flow rate of the gas using a mass-flow controller. A conventional method of supplying a processing gas by heating is a method wherein a pipe or the like which connects a reservoir vessel to a predetermined processing chamber is covered with a heating tape or the like, and an inorganic-based compound therein is heated by this heating tape through the vessel, the pipe, and the like. In heating, the inorganic-based compound in the vessel is heated to a temperature around its boiling point. The pipe is heated such that its temperature is gradually increased, from the vessel to the processing chamber, in the pipe which extends from the vessel to the processing chamber, and the temperature becomes the highest near the processing chamber. A processing gas heated and flow-adjusted as described above can be supplied into the processing chamber without being liquefied in the pipe. The supplied processing gas is used for film formation as of a predetermined wiring film or an insulating interlayer on the surface of a target object in the processing chamber using a thermal CVD process, a plasma CVD process, or the like.
On the other hand, when a predetermined film formation process is repeated several times during heating an inorganic-based compound as described above, films are formed in the processing chamber as those on the target object. These films are eventually peeled to cause particles, resulting in a decrease in yield of products. For this reason, conventionally, when the film formation process is repeated a predetermined number of times, the processing chamber is cleaned to remove a contamination source such as films. As this cleaning method, a cleaning method wherein a processing chamber is disassembled, and films formed in the processing chamber are completely removed is known. This cleaning method, however, has a problem that it requires much time for disassembling, assembling, and starting an apparatus.
In contrast to this, as a conventional film removal method, the following method is known. That is, a gas containing NF.sub.3 is fed into a processing vessel as a cleaning gas, and films deposited on a mounting table or the inner surface of the processing vessel are removed by this cleaning gas. According to this cleaning method, since the decomposition property of NF.sub.3 itself used in this method is less than desirable, a plasma is utilized. More specifically, an electrode plate is arranged at a position opposing the mounting table in the processing vessel, and a high-frequency voltage is applied across the mounting table and the electrode to produce a plasma. This plasma excites NF.sub.3 to activate it, thereby enhancing a cleaning effect. The cleaning method utilizing a plasma such as a NF.sub.3 gas has an advantage over the former method in that an apparatus need not be disassembled, thereby excessively shortening a cleaning time. On the other hand, films deposited on portions, on which the plasma is not distributed, e.g., the inner surface of the processing vessel, particularly, the inner surface of a supply head for a processing gas, are peeled during a wafer convey operation. For this reason, film fractions deposited on the bottom portion of the vessel cannot be effectively removed.
In order to more effectively clean the interior of a film forming apparatus, as disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 64-17857 and 2-77579, it is proposed that a ClF-based gas is used as a cleaning gas. According to a cleaning method using the ClF-based gas, undesired films formed on not only the surface of a mounting table but also the inner surface of a processing gas supply header and the like can be effectively and perfectly removed without using a plasma.
However, when a processing gas is supplied by the conventional method of supplying a processing gas, the processing gas may be liquefied and remain in a mass-flow controller or a valve. For this reason, when cleaning using a plasma of an NF.sub.3 gas is performed, since the chemically active NF.sub.3 gas as a plasma source may react with a remaining inorganic-based compound, this inorganic-based compound must be removed. The interior of a system is evacuated and exhausted to remove a liquid inorganic-based compound from this portion. In evacuation and exhaust, heat of vaporization is deprived from the inorganic-based compound, and its evaporation is delayed, undesirably requiring a very long time for removing the inorganic-based compound.
On the other hand, when the ClF.sub.3 gas is used as a cleaning gas, the ClF.sub.3 gas tends to be liquefied because its boiling point is about +17.degree. C. In addition, since ClF.sub.3 tends to be deposited on the inner wall of a vessel, the inner wall surface of a processing gas supply header, and the like, the ClF.sub.3 gas may be liquefied in a supply system of a cleaning gas to clog the supply system, or the ClF-based gas which is deposited on the wall surface may peel and be entrapped in a film being formed in a film formation process performed after a cleaning operation, thus causing an element defect. When the supply system temporarily clogs due to liquefaction of the gas, the supply system must be evacuated, e.g., half a day, to restore the system, resulting in a decrease in operating efficiency of the apparatus.